Traveling wave tube oscillators



g. 30, 19 0 Q G. MOURIERI ETAL 2,951,173-

TRAVELING WAVE TUBE OSCILLATORS Original Filed July 20, 1954 4Sheets-Sheet 1 m l Mn r r as w L Q C 'EORQA'S MOI/PIE? OSCAR .DOHLEP av1 34). Arm/0&0

Aug; 30, 1960 a. MOURIER ETAL ,173 TRAVELING WAVE TUBE OSCILLATORSOriginal Filed July 2 1954 4 Sheets-Sheet 2 2 70 FIG. 4 F 16 5 M I [IV70/?5 650F655 MOUP/[P 05 CAP DOHZ 5? Aug. 30, 1960 e. MOURIER ETAL ,9

' TRAVELING WAVE TUBE OSCILLATORS- flriginal Filed Ju1y20, 1954 4Sheets-Sheet 3 Aug. 30, 1960 G. MOURIER ET AL TRAVELING WAVE TUBEOSCILLATORS Fug ll INVENTORS Georges MpuRlER BY p 05% OHI ER 4Sheets-Sheet 4 United States TRAVELING WAVE TUBE ()SCILLATORS- GeorgesMourier, Llamaica, N.Y., and scar Diihler, Paris, France, assignors toCoinpagnre Generate dc Telegraphic Sans Fil, a corporation of FranceFiled Mar. 24, 1958, Ser. No. 723,467

Claims priority, application France Nov. 25, 1947 Claims. (Cl. 315-35)in an interaction space which is free of transverse electric field, asdisclosed in the copending application Serial No. 281,347, filed by B.Epsztein on April 9, 1952, assigned to the assignee of the presentinvention.

The tube according to the present invention generally comprises, withinan evacuated envelope, an interaction space free of electric field andlimited by a circularly bent structure, made of a conductive materialand comprising an ultra-high-frequency delay line, the structure beingbrought to a predetermined potential. Within this space is applied, inthe axial direction of the structure, a uniform, time-constant magneticfield, while an electron beam is injected in this space in a planeperpendicular to this direction, the velocity of the beam, which isperpendicular to this axis, and expressed in volts, being equal to thepotential of the structure concerned; thus the beam describes under theaction of the magnetic field a circular trajectory about the line axis.Electromagnetic energy is caused to propagate along the delay line withan angular phase velocity equal to the angular velocity of the beam.This results in the amplification of the ultrahigh-frequency energy and,under certain conditions, in the generation of oscillations.

An object of the invention is such an oscillator, occupying, however,less space as compared to the linear embodiment disclosed in saidEpsztein application, for similar performance.

A further object of the invention is an oscillator, operating withsmaller values of anode potential and magnetic field, than a circularM-type backward Wave oscillator, mentioned in said Epsztein application,for similar diameter and performance.

The present invention is a further development of our inventiondisclosed in copending application Serial No. 727,513, filed of evendate herewith, entitled Traveling Wave Tubes, which is acontinuation-in-part of our application Serial No. 444,558, filed July20, 1954, now abandoned, which in turn was a continuation-inpartapplication of our aforementioned application Serial No. 59,364, filedNovember 10, 1948, now abandoned. The invention disclosed in saidcopending application provides a tube comprising, inside an evacuatedenvelope, an interaction space free of electric field and limited by acircularly bent structure, made of a conductive material and comprisingan ultrahigh-frequency delay line, the structure being brought to apredetermined potential. Within this space is applied, in the directionof the structure axis, a uniform, time-constant magnetic field, while anelectron beam-is injected in this space atent 2,951,173 Patented Aug.30, 1960 ice in a plane perpendicular to this direction, the velocity ofthe beam, which is perpendicular to this axis, expressed in volts, beingequal to the potential of the structure concerned; thus the beamdescribes under the action of the magnetic field a circular trajectoryabout the tube axis.

According to the present invention, a backward wave oscillator of thetype just described comprises a delay line having propagationcharacteristics able to transmit in the desired bandwidth a wave havinga strong backward space harmonic, i.e., a harmonic traveling in adirection opposite to that of the ultrahigh-frequency energy, theangular beam velocity being made equal to angular phase velocity of thisharmonic, an ultra-highfrequency output coupled to the beam source sideof this line, and attenuating means associated with this line at a pointthereof remote from said output.

The invention will be best understood from the following description,reference being made to the accompanying drawings wherein:

Figure 1 shows a cross section of a first embodiment of the invention,used as an amplifier;

Figure 2 shows a longitudinal view of the embodiment of Figure 1;

Figure 3 illustrates the shape of the helical conductor of Figure 1;

Figure 4 shows in perspective a second embodiment of the presentinvention also used as an amplifier;

Figure 5 shows a longitudinal cross section of the em bodiment accordingto Figure 4;

Figure 6 shows a transverse cross section of the embodiment according toFigure 4;

Figure 7 shows a cross section of a third embodiment of the invention,used as an amplifier;

Figures 8 and 9 show cross sections of further embodiments of a tubesimilar to Figure 1;

Figure 10 shows a cross section taken along line 10-- 10 of Figure 11;and

Figure 11 shows an axial cross section taken along line 11-11 of Figure10 of an embodiment of backward Wave oscillator according to the presentinvention.

The tube shown .in Figures 1 to 3 is designed for operation as anamplifier; the space, free of electric field, in which the beampropagates, is included in a helix 1. This helix is Wound circularlyover two coaxial insulating rings 2 and 3 which are supported,respectively, by cross rods 4 and 5 fastened to the upper and lowercovering plates of the vacuum tight cylindrical envelope 6. The inputand output ends of the helix are connected, respectively, to theultrahigh-frequency conductors 7 and 8, which are, respectively, theinput and output for the ultra-high-frequency energy. The envelope 6 isplaced in a magnetic field directed along its axis of symmetry andsupplied by pole pieces 9 and 10. The helix is wound as a flat tape;Figure 3 shows one of its turns unrolled; the turns are of rectangularcross section, the small side of the rectangle being oriented in thedirection of the lines of force of the magnetic field as best seen inFigure 2. Between input 7 and output 8 is placed an uncoupling screen 11connected to the envelope 6, the helix assembly being surrounded by agrid 12 also connected to the envelope 6. An electron gun is placedahead of the helix input; according to the present invention, this gunis located in the vicinity of the helix periph ery, as shown in Figure1, so that the beam 13 of electrons indicated in Figure l by the dashedline travels nearer to this periphery than to the center of the helix.This gun consists of an anode 14 connected to the helix 1 and hencebrought to the potential of the latter, of a cathode 15 and of a Wehneltelectrode 16; the two latter electrodes 15 and 16 are carried by aninsulating rod 20 and brought to suitable negative potentials withrespect its central part.

to the anode, by means of conductors 17 and 18 connected to appropriatetops of the DC. power supply or source 19; the positive pole of thelatter is connected to the envelope 6 and to the helix 1 by means ofconductor 7. I perati0n.--The arrangement of the embodiment of Figures lthrough 3 operates as follows: 7

Let B be the induction of the magnetic field prevailing in the tube dueto pole pieces 9 and 10 and V the potential difierence between the helix1 and cathode 15. The electron beam, accelerated by the potential V ofthe anode 14, enters the helix with a velocity conventionally, thisvelocity v shall hereinafter be expressed by the potential V (volts), Inaccordance with Larmors law, this beam describes :a circle in the spacefree of the electric field inside the helix, with an angular velocity:

where e and m are, respectively, the charge and the mass of an electron.

If the beam is to describe a circular trajectory centered on the tubeaxis and of a given radius r, the angular velocity must be equal to w,and hence V and B must be connected by the equation:

6.10 V e I (3) There will arise an interaction between the electron beamand the ultra-high-frequency energy fed through the input 7 andpropagating within the helix 1, if the angular phase velocity of theenergy, determined by the delaying properties of the helix 1, is equalto w.

Applicants have established that, if the electron beam is .to yieldenergy to the alternating electromagnetic field, it is necessary thatthe electron gun be disposed substantially nearer to the outer peripheryof the helix than to This is why the gun 14, 15, 16 has been placed nextto the ring 3, as indicated in Figure 1.

The grid 12, which is made, for instance, of molybdenum, is for stoppingthose electrons which, traveling towards the outer part of the helix 1,might run out of the latter.

The fact that the helix 1 is of fiat cross section, with the small axisof the cross section thereof pointing in the direction of the magneticfield, makes it possible to reduce the magnitude of the radial componentof the ultrahigh-frequency field inside the helix; this component isdetrimental since it results in imparting energy to the electrons takenoff the ultrahigh-frequency field, which in turn results in a decreasein the efiiciency.

Assuming the velocity v of the electrons to be X of the velocity of thelight (V=625 volts) and assuming further that r: 3 cm., it may becalculated from Formulae l, 2 and 3 that the value for the magneticfield must be 8:28 gauss. It is seen from this example that the source19 must supply a relatively low voltage and, furthermore, that themagnet 9, may be a permanent magnet.

In the embodiment represented by Figures 4 to 6, the space free ofelectric field is included between two parallel identical disks 21 and22; one of these disks is shown in perspective in Figure 4. Each disk 21and 22, preferably of copper, displays a number of radial slots 23 whichcommunicate with cavities 24, also radial. The assembly formed by thesecavities 24 and slots 23 constitutes a delay line. In one of thesecavities, an ultrahigh-frequency electromagnetic wave is excited bymeans of the loop 25, the energy being collected at the output also bymeans of .a loop 26. The two disks 21, 22 (Figure 5) are connected bycross arms 27 made of conducting metal plate, the latter both ensuringthe rigidity of the assembly and enabling the two disks to be brought tothe same potential, so that the space between the disks is screened offfrom the action of any D.C. electric field.

In this space is disposed a gun 14, 15, 16 which is identical with thatof Figure l and is likewise placed nearer to the periphery than to thecenter of the disks 21 and '22.

The disks 21 and 22 are clamped by rings 28 against the wall of theenvelope 6 on which is also secured the collector 11, the latterextending both between the disks 21 and 22 and between the input andoutput 26. The tube structure, moreover, is the same as that of Figure1, operation being analogous thereto.

In the embodiment schematically shown in Figure 7, the fieldless spacein which the beam propagates is included between a delay line 1, on theone hand, shown again in the form, for example, of a helix though anyother type such as a vane-type delay line or one made of a sequence ofcavities may also be used, and a coaxial cylindrical electrode 31, onthe other, arranged centrally in the tube. Through the connection 32,the line 1 is brought to the potential of the electrode 31. Connection32 may alternatively be replaced by an equivalent exterior to the tubeor by separately feeding the two electrodes 1 and 31. Unlike Figure l,the beam 13 does not travel inside but outside the helix. The gun 1'4,15, 16 is arranged nearer to the helix 1 than to the electrode 31.

Furthermore, like references again denote like elements,

and the tube of Figure 7 operates as in the case of Fig- .ure 1.

Figure 8 represents a modification of the tube of Figure 1, but thismodification can, of course, be applied to the other embodiments of theinvention. At the extremity of the helix, the turns 29 are coated with asubstance that fully absorbs the ultrahigh-frequency wave; as a resultthereof, there arises along the portion of space inside the turns 29 adrift space for the electrons of the beam 12. The outermost section 3(9of the helix 1 ,is, therefore, coupled only electronically to thesection of the helix preceding the attenuator 29; the outermost .section30 may, therefore, be regarded as a distinct output circuit connected tothe output 8; it is integral with sections '-1 and 29 only forconstructive convenience.

In Figure 9 the output circuit is a resonant cavity 33. The invention isnot limited to using the described ,tube as an amplifier; it may be usedalso as an oscillator. To achieve this, one simply has either toeliminate the collector 11 so that the electrons be re-fed to the input,of the delay line, orto set up an outer feedback coupling between theoutput 8 and the input 7, or use the tube as a backward Wave oscillatorto be described more fully hereinafter.

Certain prior art devices are known which may superficially resemble thepresent application which, however,

are clearly distinguishable therefrom on the following grounds.

United States Patent 2,652,270 to R. Kompfner relates to rectilinearwave traveling tubes in which a beam propagates in an equipotentialspace, inside a rectilinear helix, interacting with the wave whichpropagates in the helix.

.The tube according to the present invention differs from tube. It hasthe advantage that it occupies less space than the rectilinearstructures alfording comparable performance. in addition, its electronicamplifying mech anism is totally different and definitely moreadvantageous as regards efficiency.

United States Patent 2,511,407 to W. Kleen et al. relates to anothertype of tube comprising two coaxial circular electrodes between which isapplied a constant, radial electric field and a magnetic field parallelto the common axis of the electrodes, across the space betwe'err theseelectrodes, which space, however, is not equipotential. A beam fed intothis space describes a circular trajectory under the action of twotransverse forces, one of which is the electric force due to the radialelectric field, the other being the Lorentz force due to the magneticfield and the velocity of the electrons. An ultrahigh-frequency wavetraveling along the delay line constituted by one of the circularelectrodes interacts with the beam, being amplified if the respectivephase and beam velocities are equal.

The tube according to the invention dilfers from this type of tube inthat the space in which the beam propagates is free of any electricfield, and that the beam velocity, expressed in volts, is equal to thepotential of the structure limiting that space. The beam describes acircular trajectory under the action of two transverse forces, oneof-which is the Lorentz force as in the former tube, the other, however,being the centrifugal force. Thus, the electrons are subjected to thesame forces as in a cyclotron, although the exchange of energy takesplace in the opposite direction. For this reason, this tubemay be termedan anti-cyclotron. It has the advantage that, assuming similarperformances, it can be built with a magnetic field much weaker andpotentials lower than in the previous tube, which facilitates thearrangement of supplying sources. Recalling that it has been calculatedhereinbefore that, under a set of predetermined conditions, the tubeaccording to the application operates under V=625 v. and 3:28 gauss, itshould be indicated by way of comparison that, for a tube according toUnited States Patent 2,511,407, assuming the same values of v and r, itis necessary to supply, respectively, 2,500 v. and 550 gauss.

Figures and 11 show, inside a vacuum-tight cylindrical envelope 106, adelay line 101, for instance, a helix, circularly wound around the axisof the tube. A decoupling screen 111, fixed to the envelope 106,protrudes radially into the tube, for mutually decoupling the twoextremities of delay line 101. An electron gun comprising a Wehneltelectrode 116, an emissive cathode 115, and an accelerating anode 114,is arranged to inject a ribbon shaped electron beam 123 through thehelix 101, nearer the outer periphery thereof than the inner one. Anoutput connection 107 is coupled to the delay line extremity adjacent tothe gun. At opposed extremity of the helix, several turns 129 are coatedwith a substance that fully absorbs the ultra-high-frequenc'y wave.

Power is supplied to the tube by a direct current source 119 having itspositive pole connected to the envelope 106 and also to the line 101,the accelerating anode 114 being, on the other hand, connected to thisline. The cathode 115 is connected through the connection 117 to anegative potential with respect to the anode 114, and the Wehneltelectrode 116 is connected through the connection 118 to a still morenegative bias potential. In this manner, the space within the turns ofthe helix 101 is equipotential, i.e., it is free of any direct currentelectric field, while the electrons emitted from the cathode 115 enterthis space with a velocity expressed in volts precisely equal to thepotential with respect to the cathode imparted to this space. Byadjusting the potential of the cathode, this velocity is adjusted to adesired value.

As shown in Figure 11, the tube is located between two polar pieces N,S, providing an axial, uniform, timeconstant magnetic field traversingthe space within the tube perpendicular to the plane of delay line andof electron beam. The sense of the magnetic field is such that electronsentering the helix 101 have their trajectories curved circularlyclockwise, and the strength of this field is such that the circulartrajectories are coaxial with the delay line. After leaving the helix at129, electrons are collected by the decoupling screen 111 operat ing ascollector. Magnetic poles N and S are excited by coils 127 and 128supplied by a direct current source 126 through a resistor 125, and theexciting current is adjustable by acting upon the resistor 125, theadjustment being ganged with the emissive cathode potential adjustmentby means of a symbolically indicated dotted mechanical connection 124.

Operation.-'Ihe tube of Figures 10 and 11 operates as follows:

Let B again be the induction of the magnetic field prevailing in thetube and V the potential difference between the helix and cathode Theelectron beam 123, accelerated by the potential V of the anode 114,enters the helix with a velocity cm./sec. X/V VOltS Conventionally, thisvelocity'v shall hereinafter be expressed by the potential V (volts).

In accordance with Larmors law, this beam again describes a circle inthe space free of electric field inside the helix, with an angularvelocity:

where e and m are, respectively the charge and the mass of an electron.

If the beam is again to describe a circular trajectory centered on thetube axis and of a given radius r, the angular velocity must be equal tow, and hence V and B must be connected by the equation:

1 M: i. B 5

Now, if the delay line has propagation characteristics such that apredetermined spatial harmonic propagates with a phase velocitycorresponding to a given phase angular velocity in the direction of thebeam while its group velocity is directed in the opposite direction,i.e., if this harmonic is a backward wave, and if the induc .tion B isso selected that w is equal to this phase angular velocity, then therewill arise an interaction between the electron beam and the backwardwave according to the well-known backward interaction process and thetube will operate as backward wave oscillator. It is known that a helixdisplays such a characteristic for some frequency bands and phasepropagation velocities. The backward wave energy, propagating within thehelix towards the output 107, is collected on the output, while anyforward propagating wave component is absorbed by the attenuation 129,as is well known in backward wave oscillator ant.

Applicants have established that, if the electron beam is to yieldenergy to the ultra-high-frequency electromagnetic field, it isnecessary that the beam circle radius r is greater than the radius ofthe circle along which extends the longitudinal axis of the helix. Thisis why the gun 114, 115 and 116 has been placed so that the beam 123passes nearer the outer periphery of the helix 101 than the inner one.

The tube oscillates at such a frequency that the phase angular velocity,which, as is well known, depends on frequency, is equal to the beamangular velocity, as defined by Formula 5. Since this angular velocityis determined by the magnetic field B, a frequency variation will beobtained by varying the magnetic field by means of resistor 125. If thebeam, nevertheless, is to continue describing, in a broad frequencyband, a concentric circular trajectory of constant radius r, it isnecessary to accompany this magnetic field variation with a variation ofthe accelerating potential V, by means of potential supply variation ofthe connection 1-17, so as to satisfy the law expressed by Formula 6.For this purpose, the adjustments of B and V are preferably ganged,ismindicated by the symbolical mechanical connection The backward waveoscillator according to the present invention differs from thewell-known O-type backward wave oscillator in that while the space inwhich the beam propagates is in both cases free of electric field, thebeam describes a circular trajectory in the tube according to thepresent invention, in contradistinction with the linear trajectory ofthe O-type backward wave oscillator.

.Therefore, for a given performance, the oscillator according to thepresent invention occupies less space. Moreover, with respect towell-known circular M-type backward type oscillator, the presentinvention differs in that the beam moves under the action of atransverse Lorentz force and of an opposite centrifugal force, in aspace free of electric field, in contradistinction to two crossedelectric and magnetic fields of an M-type oscillator, in which the beammoves under the action of a transverse Lorentz force and of an oppositeelectric force. Assuming similar size and performance, the oscillatoraccording to the present invention can be built with a magnetic fieldmuch weaker and potentials lower than in the previous tube, whichfacilitates the arrangement of the supply sources. For instance,assuming the velocity v of the electrons to be 15,000 km./sec. and theradius r=3 cm., it may be calculated from Formulae 4, 5 and 6 that B=28gauss and V:625 volts. A calculation shows that for a circular M-typebackward wave oscillator, assuming the same values of -v, r andgenerated frequency, it is necssary to supply, respectively, 550 gaussand 2500 v0 ts.

While the backward wave oscillator has been specifically describedherein only with reference to Figures 10 and 11, it is understood thatthe other embodiments described in connection with Figures 1 through 9may also be operated as such by adapting the same in a correspondingmanner, i.e., provide therefor the attenuating or absorbing means inconnection with the end of the delay line opposite the electron gun, byremoving any output coupling at this end unless it is connected with anexternal attenuation or absorbing means, and by suitably adjusting theparameters to provide the desired operational effect.

We claim:

1. An electron discharge tube comprising, in an evacuated envelope, acurved conductive structure defining a circular electron and waveinteraction duct having an output and delay elements forultra-high-frequency Wave energy propagating in said duct, a terminalconnection to said structure for applying a potential to determine anequipotential throughout said duct, an electron gun positioned at oneend of said duct adjacent said output to emit a beam of electrons intosaid duct in a plane perpendicular to the axis of curvature of saidstructure at a velocity having a resultant directed perpendicularly tosaid axis and a value expressed in volts substantially equal to saidpotential, means for establishing in said duct a uniform magnetic fieldhaving its lines of force directed parallel to said axis, the delayingcharacteristics of said delay elements and the magnitude of saidinduction being such as to cause the angular velocity of phasepropagation, in the same sense as said beam of electrons, ofultra-high-frequency wave energy propagating in said duct in theopposite direction to said beam of electrons to be substantially equalto the angular velocity of said electrons, means associated with saidstructure at a point thereof remote from said electron gun forattenuating Ill ultrahigh-frequency wave energy, and means forcollecting wave energy at said output.

2. A microwave oscillator comprising first means including an electronsource and a collector electrode defining therebetween a path ofelectron flow, a wave guiding structure positioned along said path inwhich there is induced by the electron flow an electromagnetic wavewhich travels in a direction opposite that of electron flow, meanscoupled to the said wave guiding structure for abstracting the inducedwave, potential supplying means for imparting to the space of theelectron flow in-said path an equipotential equal to said flow velocityexpressed in potential units, and means for curving the electron flow insaid path in a predetermined plane comprising means for establishing anessentially uniform magnetic field having its lines of force directedperpendicular to said plane and acting on said flow.

3. An oscillator as claimed in claim 2, further comprising means forchanging the frequency of the induced wave comprising means for varyingthe strength of said magnetic field.

4. An oscillator as claimed in claim 3, further comprising acceleratingmeans for varying said electron flow velocity.

5. An oscillator as claimed in claim 2, wherein the axis of said guidingstructure is circularly curved along a circle of predetermined radius,and wherein said electron source is so positioned that the radius ofsaid electron flow circular path is greater than said longitudinal axis.circle radius.

6. An ultra-high-frequency oscillator tube adapted to produceoscillations of a frequency which is adjustable at will over arelatively wide, uninterrupted band, said tube comprising a circularlycurved delay line having a geometrically periodical structure, anelectron emissive source .at least at the other end of said line forabsorbing ultrahigh-frequency energy propagated along said line in thesame direction as the beam thereby substantially to prevent reflectionsfrom said other end and thus to render said line electrically aperiodicwithin the limit of said band, means for directing-said beam ofelectrons along a path substantially parallel to said line and at avelocity substantially equal to the apparent or phase velocity of anegative space harmonic of electromagnetic wave energy propagating insaid line in the opposite direction to the beam, thereby to causeinteraction between said beam and said negative space harmonic forsustained flow of energy toward said electron emissive source, meansadjacent said source for transferring said energy to an external loadcircuit, potential supplying means for imparting to the space betweensaid beam and said line an equipotential equal to said beam velocityexpressed in potential units, and means for circularly curving the pathof said electron beam to be substantially coaxial with said delay lineincluding means for establishing an essentially uniform magnetic fieldhaving its lines of force directed perpendicular to said curvature planeand acting on said beam.

7. An ultrahigh-frequency oscillator tube adapted to produceoscillations of a frequency which is adjustable at will over arelatively wide band, said tube comprising a wave-guiding structurehaving effectively a first end and a second end, cathode means foremitting electrons adapted to propagate from said first end toward saidsecond end along said wave-guiding structure in coupled relationshiptherewith to thereby induce electromagnetic Wave energy in saidwave-guiding structure and to interact with a space harmonic thereof,means for directing said electrons to propagate along said wave-guidingstructure in coupled relationship therewith in'a direction from 9 saidfirst end toward said second end of said wave-guiding structure and at avelocity substantially equal to the apparent or phase velocity of anegative space harmonic of the electromagnetic wave energy propagatingin said wave-guiding structure in the opposite direction to the flow ofsaid electrons, thereby to cause interaction between said electrons andsaid negative space harmonic for sustained flow of energy toward saidcathode means, means near said first end of said wave-guiding structureand operatively connected thereto for transferring said energy to anexternal load circuit, means for producing in the space of propagationof said electrons an equipotential equal to the flow velocity thereofexpressed in potential units, and means for curving the electron flow ina predetermined plane including means for establishing an essentiallyuniform magnetic field having its lines of force directedperpendicularly to said plane and acting on said electron flow.

8. An ultra-high-frequency oscillator tube according to claim 7, furthercomprising means at least near one end of said wave-guiding structure tominimize reflections thereat of said induced electromagnetic wave.

9. A traveling wave, ultra-high-frequency electron discharge deviceadapted to produce oscillations of a frequency which is adjustable atwill over a relatively wide band, said tube comprising a wave-guidingstructure having elfectively a first end and a second end, cathode meansin said system for emitting electrons adapted to propagate from saidfirst end toward said second end along said waveguiding structure and tointeract with a space harmonic thereof, means for directing saidelectrons to propagate along said wave-guiding structure in coupledrelationship therewith in a direction from said first end toward saidsecond end to said wave-guiding structure and at a velocitysubstantially equal to the apparent or phase velocity of a negativespace harmonic of the electromagnetic wave energy propagating in saidwave-guiding structure in the opposite direction to the flow of saidelect trons, thereby to cause interaction between said electrons andsaid negative space harmonic for sustained flow of energy toward saidcathode means including means for producing in the space of propagationof the electrons an equipotential equal to the flow velocity of theelectrons expressed in potential units, and means producing anessentially uniform magnetic field having its lines of force directedperpendicularly to a predetermined plane and acting on electron =fl0w tocurve the same in said plane, and means near said first end of saidwave-guiding structure and operatively connected thereto fortransferring said energy to an external load circuit.

10. A microwave oscillator comprising first means including an electronsource and a collector electrode defining therebetween a path ofelectron flow, a wave-guiding structure positioned along said path inwhich there is induced by the electron flow an electromagnetic wavewhich travels in a direction opposite that of electron flow, meanscoupled to said wave-guiding structure for abstracting the induced wave,means for producing in the space of electron flow an equipotential equalto the flow velocity of electrons expressed in potential units, andmeans for curving the electron flow in said path in a predeterminedplane including means for establishing an essentially uniform magneticfield having its lines of force directed perpendicularly to said planeand acting on said electron flow.

References Cited in the file of this patent UNITED STATES PATENTS2,511,407 Kleen et al. June 13, 1950 2,617,961 Bruck Nov. 11, 19522,702,370 Lerbs Feb. 15, 1955 2,775,721 Dench Dec. 25, 1956 2,786,959Warnecke et a1 Mar. 26, 1957 2,812,468 Robertson No 5, 1957

